Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• High contact resistance at metal-semiconductor interfaces limits field-effect transistor performance, especially with shrinking device dimensions.
• Two-dimensional (2D) materials like molybdenum disulfide (MoS2) are promising for ultrathin transistors, but suffer from high contact resistance.
• Existing van der Waals contacts often involve transferred materials or multilayered 2D semiconductors, leaving a gap for monolayer applications.

Purpose of the Study:

• To demonstrate ultraclean van der Waals contacts between a 3D metal and monolayer 2D transition-metal dichalcogenides.
• To investigate the interface properties and contact resistance of novel metal-semiconductor junctions.
• To enable high-performance field-effect transistors using 2D materials.

Main Methods:

• Fabrication of contacts using 10nm indium capped with 100nm gold on monolayer MoS2.
• Annealing at 200°C to form an indium-gold solid solution.
• Characterization using scanning transmission electron microscopy (STEM) to confirm interface quality and bonding.

Main Results:

• Achieved atomically sharp, ultraclean interfaces with van der Waals-type bonding between metal and monolayer MoS2.
• Measured contact resistance of 3000 ± 300 Ω·µm for monolayer MoS2 and 800 ± 200 Ω·µm for few-layered MoS2.
• Demonstrated high field-effect transistor mobility (167 ± 20 cm²/Vs) and low contact resistance on other 2D materials like NbS2, WS2, and WSe2.

Conclusions:

• Successfully realized ultraclean van der Waals contacts on monolayer 2D semiconductors using a simple, standard laboratory method.
• The developed contact strategy significantly reduces contact resistance, paving the way for high-performance 2D electronic devices.
• This approach offers a versatile route for fabricating high-quality interfaces for various 2D transition-metal dichalcogenides.